Parallel hybrid vehicle optimal storage system

ABSTRACT

The present invention is a method and apparatus by which power is controlled in a hybrid electric vehicle such that high levels of performance and efficiency are realized. The present invention includes a method and apparatus developed to optimize the use of energy in a hybrid vehicle application from the hybrid energy storage device. The method and apparatus of the present invention is particularly useful with energy storage devices there the energy state, such as the state of charge, is readily determined by an easily measured attribute. Ultracapacitors and hydraulic storage cylinders are examples of the types of energy storage devices to which the present invention may be applied.

TECHNICAL FIELD OF THE INVENTION

The present invention is in the field of hybrid vehicles, such as hybridelectric vehicles.

BACKGROUND AND SUMMARY OF THE INVENTION

The present invention relates to an environmental friendly vehicle. Moreparticularly, the present invention relates to hybrid vehicles, such ashybrid electric vehicles (HEVs).

Hybrid electric vehicles include an internal combustion engine and atleast one electric motor powered by a battery array. The HEV of thepresent invention uses an engine in combination with an electric motor.An energy storage device is also used to store energy for driving theelectric motor. The engine, preferably in conjunction with a generator(for series drive embodiment or without for a parallel embodiment), andthe energy storage device work in combination to provide energy forpowering the vehicle motor. A series HEV typically uses an engine with agenerator (APU/PPU) to supply electricity to the motor and the energystorage system. A parallel HEV has a direct mechanical connectionbetween the engine and the wheels. The use of electric powersubstantially cuts down on chemical emissions and vastly improves fueleconomy.

In a parallel type hybrid electric vehicle, both the internal combustionengine and the electric motor are coupled to the drive train viamechanical means. The electric motor may be used to propel the vehicleat low speeds and to assist the internal combustion engine at higherspeeds. The electric motor may also be driven, in part, by the internalcombustion engine and be operated as a generator to recharge the batteryarray.

In a series type hybrid electric vehicle, the internal combustion engineis used only to run a generator that charges the battery array. There isno mechanical connection of the internal combustion engine to thevehicle drive train. The electric traction drive motor is powered by thebattery array and is mechanically connected to the vehicle drive train.

Although HEVs have been previously known, the HEV technology of thepresent invention provides significant advantages of providing a viableHEV technology that allows for a high performance HEV with a uniquemanagement of the charge and energy distribution system.

Other features of the invention will become apparent as the followingdescription proceeds and upon reference to the drawings.

In general terms, the present invention includes an energy storagesystem, the energy storage system adapted to accept energy so as to becapable of discharging and accepting energy through a series ofdischarge and energy acceptance events, and having a maximum energystate level and an actual minimum energy state level; and wherein thepower unit and the energy storage system provide electricity to theelectric motor for powering the vehicle; and an energy storagecontroller programmed to control the energy storage system by setting anartificial minimum energy state level to an initial level above theactual minimum energy state level, and, during a series of discharge andenergy acceptance events, to be able to adjust the artificial minimumenergy state level such that:

(a) in the case where a discharge and energy acceptance event results inthe acceptance of insufficient energy to replenish the energy storagesystem to the maximum energy state level, the artificial minimum energystate level is raised; and

(b) in the case where a discharge and energy acceptance event results inthe acceptance of sufficient energy to replenish the energy storagesystem to the maximum energy state level, the artificial minimum energystate level is lowered.

The energy storage controller preferably is further programmed tocontrol the energy storage system by restricting the raising of theartificial minimum energy state level beyond a predetermined level belowthe maximum energy state level. It is also preferred that the energystorage controller is further programmed to control the energy storagesystem by restricting the lowering of the artificial minimum energystate level beyond a predetermined level above the actual minimum energystate level.

The energy storage system may comprise energy storage systems of anytype capable of energy discharge acceptance events such as thoseselected from the group of: (1) at least one ultracapacitor and (2) atleast one hydraulic cylinder. The energy storage system may alsocomprise an internal combustion engine and a generator adapted toprovide energy to the energy storage system, such as electric energy.

The present invention also includes a method of controlling an energystorage system, the method comprising: providing an energy storagesystem electrically coupled to a power conversion device, the energystorage system adapted to recapture energy from the power conversiondevice so as to be capable of discharging and recapturing energy througha series of discharge and energy acceptance events, and having a maximumenergy state level and an actual minimum energy state level; and theenergy storage system providing energy to the power conversion device,and the power conversion device adapted to supply energy to the energystorage system; and an energy storage controller programmed to controlthe energy storage system by setting an artificial minimum energy statelevel to an initial level above the actual minimum energy state level,and, during a series of discharge and energy acceptance events, to beable to adjust the artificial minimum energy state level such that:

(a) in cases where a discharge and energy acceptance event results inthe acceptance of insufficient energy to recharge the energy storagesystem to the maximum energy state level, raising the artificial minimumenergy state level; and

(b) in cases where a discharge and energy acceptance event results inthe acceptance of sufficient energy to recharge the energy storagesystem to the maximum energy state level, lowering the artificialminimum energy state level.

The present invention also includes a method and apparatus by whichpower is controlled in a hybrid electric vehicle such that high levelsof performance and efficiency are realized. The invention relatesspecifically to the alternate energy source and optimization of its use.

The present invention includes a method and apparatus developed tooptimize the use of energy in a hybrid vehicle application from thehybrid energy storage device.

The method and apparatus of the present invention is particularly usefulwith energy storage devices where the state of charge is readilydetermined by an easily measured attribute. Ultracapacitors andhydraulic storage cylinders are examples of the types of energy storagedevices to which the present invention may be applied.

The state of charge, or energy level, is proportional to the voltage ofthe ultracapacitor or the pressure of the hydraulic cylinder. The methodand apparatus of the present invention is particularly well-suited tohybrid vehicle applications where the hybrid power is primarily utilizedduring acceleration and deceleration.

The present invention is particularly well-suited to hybrid electricvehicle applications where the hybrid power is primarily used duringacceleration and deceleration. The method includes three fundamentalfeatures which may be illustrated with respect to a parallel hybridelectric vehicle using storage of the type described above: (1) energyis expended from the hybrid energy storage device at a predeterminedrate until a minimum energy level target is reached, whereupon theenergy storage device is later replenished with energy from the vehicle.There is an equilibrium of energy expended to that replenished that willresult; (2) the minimum energy target is continuously adjusted such thatthat equilibrium can be maintained at a higher power state of thestorage device; and (3) replenishing the energy storage device with boththe kinetic energy from the vehicle while decelerating, and with energydrawn from the primary power source of the vehicle during opportuneevents (i.e., typically when the vehicle is cruising or coasting, suchas when moving downhill or otherwise not in need of accelerating power).

In one aspect of the invention, during vehicle acceleration, when hybridenergy is desired, energy is expended from the hybrid energy storagedevice at a pre-determined rate until a target minimum energy level isreached. Subsequently, during deceleration the recapture of energy fromthe kinetic energy of the vehicle to replenish the storage device ismaximized. The more energy recovered in the energy storage device priorto a given acceleration event, the more energy that can be expended inthat acceleration event.

In contrast to earlier methods, the method of the present inventionfeatures a system that is self-adjusting and will seek equilibrium withthe energy balance of what is expended and replenished. The method ofthe present invention does not utilize fixed relationships between thehybrid storage level and vehicle state such as, for example, energylevel and vehicle speed. Accordingly, changes to the energy and powerrequirements of the vehicle due to variations in terrain, drive cycle,vehicle weight, tire pressure, and the like will not adversely affectits performance. The hybrid drive following the minimum target levelstrategy will naturally adjust its contribution to maintain consistentvehicle performance and operator/passenger feel.

The rate at which energy is expended from the energy storage device maybe any rate, so long as it is consistent.

The present invention also includes the adjustment of the minimum energytarget level continuously so the energy storage device and correspondingpower conversion system maintain a higher power state at equilibrium.For the energy storage devices described herein, the power is a productof the potential and flow. Accordingly, for a given flow, a higherpotential will provide higher power.

There are two advantages to maintaining a higher potential. First,available hybrid power will be more consistent with peak power despitedrive cycles with low vehicle kinetic energy. Second, for powers lessthan peak power of the system, a higher potential means less flowrequired. For energy storage devices such as Ultracapacitors andhydraulic cylinders, and the corresponding power conversion systems,lower flow means less energy loss as heat and thus higher efficiency. Inaddition, lower heat loss means that cooling systems do not work ashard.

In operation, each time the hybrid vehicle comes to rest at zero speed,and accounting for settling time of the storage device, the energy levelof the storage device can be evaluated to see if the level has reachedmaximum capacity. If not, the minimum energy target level can then beraised. If so, the minimum target level can be lowered. This processrepeats until equilibrium is reached. Anticipating disruptions toequilibrium will maximize the effectiveness of the strategy.

In another aspect of the invention, the higher energy level of thestorage device prior to acceleration, the more that can be expended byway of hybrid assist. Striving for maximum hybrid contribution, twoapproaches as presented for increasing the amount of energy availableprior to an acceleration event, beyond what is recovered during vehicledeceleration with regenerative braking.

One approach is to “siphon” power from the primary power source while itis operating at high efficiency or while it could be made to operatemore efficiently. That is, to charge the energy storage system from theprimary power source at a nominal rate that is just enough so as not todrastically alter its operation. Examples of operating points ideallysuited for siphoning include when the vehicle is cruising at a steadystate where fuel economy is relatively high and when the vehicle isstopped with the engine at idle doing little work with fixed operatingoverhead.

A small siphon charge over a period of time can significantly increasethe energy level of the storage device. As a means to preserve storagecapacity for the vehicle deceleration with regenerative braking, atarget energy level is set below which siphoning is permitted. Thetarget energy level is established in some relation to the kineticenergy of the vehicle.

The other approach is to simulate the drag normally associated withinternal combustion engines at closed throttle through the use ofregenerative braking. By applying a moderate level of regenerativebraking when the operator lifts from the accelerator pedal, the vehiclewill decelerate slightly and the energy storage device will be chargedat a low rate.

The present invention allows for consistency in the power output duringacceleration which is proportionate to apparent power demand.

The method and apparatus of the present invention feature the functionof certain algorithms for system control. These algorithms use real-timeinputs from the vehicle systems and provide real-time outputs forcontrol of vehicle systems. The principal function of the presentinvention is to supplement the primary power source in a manner that isrelatively transparent to the operator while preserving standard,consistent vehicle performance. This allows for consistent feel to theoperator and the passengers as the vehicle accelerates and decelerates.

The present invention features a control algorithm that maintains thestate of charge of the energy storage device (such as one or moreultracapacitors) within a pre-determined range as the vehicle proceedsthrough a number of energy expending and recapture events which mayinvolve net energy loss or net energy gain.

The present invention is an improvement over the technology described inU.S. Pat. Nos. 6,484,830 and 6,651,759, which are hereby incorporatedherein by reference, and which may be used with hybrid electric vehiclesand drive systems as described therein as an example.

In general terms, the present invention includes a hybrid electricvehicle comprising a drive train; an electric motor for driving thedrive train; a power unit electrically coupled to the electric motor; anelectric energy storage system electrically coupled to the electricmotor, the electric energy storage system adapted to recapture energyfrom the braking of the vehicle so as to be capable of discharging andrecapturing energy through a series of discharge and energy recaptureevents, and having a maximum charge level and an actual minimum chargelevel; and wherein the power unit and the electric energy storage systemprovide electricity to the electric motor for powering the vehicle; andan electric energy storage controller programmed to control the electricenergy storage system by setting an artificial minimum charge level toan initial level above the actual minimum charge level, and, during aseries of discharge and energy recapture events, to be able to adjustthe artificial minimum charge level such that: (a) in the case where adischarge and energy recapture event results in the recapture ofinsufficient energy to recharge the electric energy storage system tothe maximum charge level (e.g., the energy discharged in an accelerationand the energy recaptured from braking after that acceleration), theartificial minimum charge level is raised; and (b) in the case where adischarge and energy recapture event results in the recapture ofsufficient energy to recharge the electric energy storage system to themaximum charge level, the artificial minimum charge level is lowered.

It is preferred that the electric energy storage controller is furtherprogrammed to control the electric energy storage system by restrictingthe raising of the artificial minimum charge level beyond apredetermined level below the maximum charge level.

It is preferred that the electric energy storage controller is furtherprogrammed to control the electric energy storage system by restrictingthe lowering of the artificial minimum charge level beyond apredetermined level above the actual minimum charge level.

The present invention may be applied to any energy storage system,although, in the case of a hybrid electric vehicle, it is preferred thatthe energy storage system is a bank of Ultracapacitors, and that thissystem be used in association with an internal combustion engine and agenerator adapted to charge the energy storage system with electricalenergy.

Another aspect of the present invention is a hybrid electric vehiclecomprising a drive train; an electric motor for driving the drive train;a power unit electrically coupled to the electric motor; an electricenergy storage system electrically coupled to the electric motor, theelectric energy storage system adapted to recapture energy from thebraking of the vehicle so as to be capable of discharging andrecapturing energy through a series of discharge and energy recaptureevents, and having a maximum charge level and an actual minimum chargelevel having a working range therebetween and which working is definedat its lower end by an artificial minimum charge level; and wherein thepower unit and the electric energy storage system provide electricity tothe electric motor for powering the vehicle; and an electric energystorage controller programmed to control the electric energy storagesystem by setting an artificial minimum charge level to an initial levelabove the minimum charge level, and, during a series of discharge andenergy recapture events, to be able to adjust the artificial minimumcharge level such that the working range of the electric energy storagesystem is biased toward the maximum charge level over the series ofdischarge and energy recapture events.

The present invention also includes a method of controlling an energystorage system, the method comprising: providing an electric energystorage system electrically coupled to the electric motor, the electricenergy storage system adapted to recapture energy from the braking ofthe vehicle so as to be capable of discharging and recapturing energythrough a series of discharge and energy recapture events, and having amaximum charge level and an actual minimum charge level; and wherein thepower unit and the electric energy storage system provide electricity tothe electric motor for powering the vehicle; and an electric energystorage controller programmed to control the electric energy storagesystem by setting an artificial minimum charge level to an initial levelabove the actual minimum charge level, and, during a series of dischargeand energy recapture events, to be able to adjust the artificial minimumcharge level such that: (a) in the case where a discharge and energyrecapture event results in the recapture of insufficient energy torecharge the electric energy storage system to the maximum charge level,raising the artificial minimum charge level; and (b) in the case where adischarge and energy recapture event results in the recapture ofsufficient energy to recharge the electric energy storage system to themaximum charge level, lowering the artificial minimum charge level.

The method of the present invention thus maintains the charge level ofthe energy storage device, such as an ultracapacitor, at a level in thehigher end of the charge range over time.

Other objects, features, and advantages of the present invention willbecome apparent to those skilled in the art from the following detaileddescription and accompanying drawings. It should be understood, however,that the detailed description and specific examples, while indicatingpreferred embodiments of the present invention, are given by way ofillustration and not limitation. Many modifications and changes withinthe scope of the present invention may be made without departing fromthe spirit thereof, and the invention includes all such modifications.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic of an energy storage system describing the extentof the charge and discharge of the energy storage system as it proceedsthrough a series of energy discharge and recapture events.

FIG. 2 is a schematic of an energy storage system describing the extentof the charge and discharge of the energy storage system as it proceedsthrough a series of energy discharge and recapture events while beingcontrolled by the method and system of one embodiment of the presentinvention.

FIG. 3 shows a schematic of a hybrid electric vehicle in accordance withone embodiment of the present invention.

FIG. 4 is a schematic representation of the control nodes that may beused in accordance with one embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In accordance with the foregoing summary of the invention, the followingpresents a detailed description of the preferred embodiments, which areconsidered to be the best mode thereof.

Energy storage devices like the ultracapacitor and hydraulic cylindercan be charged or discharged only with a change in energy potential.Energy storage is typically sized for the recapture of vehicle (system)kinetic energy from some maximum speed, representing a full chargeevent, referred to herein as an energetically favorable event.

A full discharge/charge event of the energy storage device will utilizethe absolute maximum and minimum energy levels (potentials) of thedevice. This is the full working range of the device. Partialdischarge/charge events will utilize only a portion of the full workingrange. These typically will be events wherein the energy expended willbe only partially replaced by the energy recaptured during regenerativebraking, referred to herein as an energetically disfavorable event. Theworking range of partial discharge and charge events will tend towardthe absolute minimum potential of the energy storage. The presentinvention takes advantage of the fact that a working range nearer theabsolute maximum potential has an advantage over a working range nearerthe absolute minimum. In order to move the working range toward themaximum in partial charge events, an artificial minimum level must beutilized rather than the absolute. The artificial minimum must be setbetween the absolute minimum and the absolute maximum. The artificialminimum is adjusted upward after a charge event if the absolute maximumpotential is not reached (i.e., after an energetically disfavorableevent). The adjustment upward may be a constant increment value.Conversely, the artificial minimum is adjusted downward toward theabsolute minimum after a charge event if the maximum absolute potentialis reached (i.e., after an energetically favorable event). Theadjustment downward may also be a constant decrement value. Theartificial minimum level is adjusted after a charge event as long as theenergy state of the storage device has not reached or exceeded theabsolute maximum.

The present invention accordingly allows one to achieve a balancebetween energy expended and replenished. That is, the net charge energyought to be greater than or equal to the discharge energy of the storagedevice. A net loss of energy charge-to-discharge will tend to drive theworking range of the device to the minimum potential.

A portion of the vehicle (system) kinetic energy is unavailable forcharging the energy storage because of electrical and mechanical losses.To help achieve the balance between energy expended and replenished, thepresent invention attempts to limit the discharge energy to less thanthe charge energy. One approach is to discharge to vehicle speed A andcharge from vehicle speed B where speed A is less than B. Another is tolimit the discharge maximum power to less than the maximum charge power.

The present invention may also be applied to limit the artificialminimum to some maximum value so as to preserve a determined workingrange.

The present invention thus utilizes a strategy that optimizes the energystorage use over successive discharge/charge events. The average use isoptimized not necessarily any one event.

Level determination and adjustment of the energy storage can beachieved, for instance, through either measuring energy potential orcounting energy units in and out.

The process of limit adjustment will tend to preserve the optimalworking range of an energy storage bank regardless of the capacity.Ideally and preferably, one may initialize the artificial minimum limitto the midpoint of the absolute minimum and maximum levels.

Without using the method of the present invention, the energy storageutilization will be driven toward the low power range of the storagedevice. This is especially the case with energy storage devices withmore capacity than the kinetic energy of the vehicle or system.

Enhancement of the strategy is recommended to ensure all requests forpower are satisfied with some hybrid power regardless of the energylevel of the storage device. Also, in cases where a future charge eventwill be more favorable in terms of energy recapture, a lower artificialminimum can be set to allow more energy than normal to be expended atpresent. This may require a “fuzzy” or non-strict implementation of theartificial minimum. Fuzzy logic and/or expert systems can be utilized topredict future behavior based on past and present behavior. This may beespecially successful with vehicles and systems with specific andconsistent missions. In the case of vehicles, the use of GPS satellitedata can provide valuable information to this end, such as overall routelength, numbers and distance between acceleration and decelerationevents, etc.

FIG. 1 is a schematic of an energy storage system describing the extentof the charge and discharge of the energy storage system as it proceedsthrough a series of energy discharge and energy recapture events. As maybe appreciated from this Figure, an electric energy storage device(i.e., a capacitor; represented by a cylinder) proceeds through a seriesof energy discharge and energy recapture events while acceleration ofthe vehicle and regenerative braking occurs. FIG. 1 shows that, ininstances where there is no control over the lower charge limit of thecapacitor, the charge of the capacitor continues to drop over successiveenergy discharge and energy recapture events that are energeticallydisfavorable (i.e., where the output of energy upon acceleration exceedsthe energy recaptured upon regenerative braking).

In contrast, FIG. 2 is a schematic of an energy storage systemdescribing the extent of the charge and discharge of the energy storagesystem as it proceeds through a series of energy discharge and recaptureevents while being controlled by the method and system of one embodimentof the present invention. FIG. 2 shows that in accordance with thepresent invention the lower charge limit of the capacitor is controlledand adjusted. As shown in FIG. 2, the charge of the capacitor drops inthe case of an energy discharge and energy recapture event that isenergetically disfavorable (i.e., where the output of energy uponacceleration exceeds the energy recaptured upon regenerative braking).In such cases, the controller of the present invention adjusts anartificial lower charge limit upward and above the absolute lowestcharge level (i.e., the level of complete discharge). For instance, FIG.2 shows a fully charged capacitor which proceeds through a fulldischarge event followed by a partially charging capture event.Thereafter, an artificial lower charge limit is set such that asubsequent discharge prevents complete discharging of the capacitor.During a subsequent discharge event, the capacitor is restricted fromdischarging below the artificial lower charge limit. Subsequently, andas this event is energetically unfavorable, the artificial lower chargelimit is again raised from the previously set artificial lower chargelimit. This process may be allowed to continue until an energy dischargeand energy recapture event results in the complete recharging of thecapacitor. In this instance, the artificial lower charge limit islowered to a point lower than previously set, and above the absolutelowest charge level.

The apparatus and methods of the present invention may be produced usingmicroprocessors and computer languages known and used in the art.

An example of an algorithm in pseudo code showing the adjustment of theartificial minimum charge level with the energy storage potentialmeasured following a deceleration event is shown below. This may be usedto bring about the control of the energy storage system of the presentinvention and may be understood by reference to the following logic foradjusting the minimum charge level with optional reference to systemtorque:PSEUDO CODE for ADJUSTING ARTIFICIAL MINIMUM CHARGE LEVELEnergy Storage Potential Measured Following a Deceleration Event

-   SIMPLEST FORM    The following algorithm is executed every iteration of the control    loop. Ideally, the control loop is executed several times per    second.    The variables, constants, and flags indicated in the algorithm are    defined as follows:-   VehicleSpeed, variable, measure of vehicle ground speed.-   PotentialLevel, variable, measure of energy storage potential (e.g.    voltage).-   TargetLevel, variable, artificial minimum potential level to reach    during discharge events, can be initialized to the midpoint between    MAX_LEVEL and MIN_LEVEL.-   Prev_At_Speed, flag, indicates if vehicle has reached a    pre-determined speed to trigger the level adjustment calculation    after next deceleration event, initialized to false.-   MIN_LEVEL, constant, the lowest potential level allowed to be    reached, oftentimes the absolute minimum potential of the storage    device.-   MAX_LEVEL, constant, the highest potential level to be reached,    oftentimes the absolute maximum potential of the storage device.-   MAX_TARGET_LEVEL, constant, the highest artificial minimum potential    allowed, set to preserve a minimum working range.-   LEVEL_STEP, constant, the step value for target level adjustment,    could also be a parameter resulting from a transfer function.-   LEVEL_ADJ_THRESHOLD, constant, minimum speed threshold before the    level adjustment calculation can be triggered.-   AT_REST_THRESHOLD, constant, speed threshold below which the vehicle    is considered to be at rest.

INITIALIZE: . . . Prev_At_Speed = FALSE TargetLevel = ((MAX_LEVEL −MIN_LEVEL) / 2) + MIN_LEVEL . . . End INITIALIZE CONTROL LOOP: . . . IfVehicleSpeed > LEVEL_ADJ_THRESHOLD Then Prev_At_Speed = TRUE End If IfVehicleSpeed < AT_REST_THRESHOLD Then If Prev_At_Speed = TRUE Then IfPotentialLevel >= MAX_LEVEL Then TargetLevel = TargetLevel − LEVEL_STEPIf TargetLevel < MIN_LEVEL Then TargetLevel = MIN_LEVEL End If ElseTargetLevel = TargetLevel + LEVEL_STEP If TargetLevel > MAX_TARGET_LEVELThen TargetLevel = MAX_TARGET_LEVEL End If End If Prev_At_Speed = FALSEEnd If End If . . . Go to CONTROL LOOP

An example of an algorithm in pseudo code showing the adjustment of theartificial minimum charge level with the energy storage potentialmeasured prior to an acceleration event is shown below.PSEUDO CODE for ADJUSTING ARTIFICIAL MINIMUM CHARGE LEVELEnergy Storage Potential Measured Prior to an Acceleration Event

-   SIMPLEST FORM    The following algorithm is executed every iteration of the control    loop. Ideally, the control loop is executed several times per    second.    The variables, constants, and flags indicated in the algorithm are    defined as follows:-   VehicleSpeed, variable, measure of vehicle ground speed.-   PotentialLevel, variable, measure of energy storage potential (e.g.    voltage).-   TargetLevel, variable, artificial minimum potential level to reach    during discharge events, can be initialized to the midpoint between    MAX_LEVEL and MIN_LEVEL.-   Prev_At_Speed, flag, indicates if vehicle has reached a    pre-determined speed to trigger the level adjustment calculation    after next deceleration event, initialized to false.-   MIN_LEVEL, constant, the lowest potential level allowed to be    reached, oftentimes the absolute minimum potential of the storage    device.-   MAX_LEVEL, constant, the highest potential level to be reached,    oftentimes the absolute maximum potential of the storage device.-   MAX_TARGET LEVEL, constant, the highest artificial minimum potential    allowed, set to preserve a minimum working range.-   LEVEL_STEP, constant, the step value for target level adjustment,    could also be a parameter resulting from a transfer function.-   LEVEL_ADJ_THRESHOLD, constant, minimum speed threshold before the    level adjustment calculation can be triggered.-   AT_REST_THRESHOLD, constant, speed threshold below which the vehicle    is considered to be at rest.-   TorqueRequest, variable, indicator of drive torque requested of the    hybrid system.-   ZERO_TORQUE, constant, torque threshold below which the hybrid drive    applies no driving torque.

INITIALIZE: . . . Prev_At_Speed = FALSE TargetLevel = ((MAX_LEVEL −MIN_LEVEL) / 2) + MIN_LEVEL . . . End INITIALIZE CONTROL LOOP: . . . IfVehicleSpeed > LEVEL_ADJ_THRESHOLD Then Prev_At_Speed = TRUE End If IfVehicleSpeed < AT_REST_THRESHOLD Then If Prev_At_Speed = TRUE Then IfTorqueRequest > ZERO_TORQUE Then If PotentialLevel >= MAX_LEVEL ThenTargetLevel = TargetLevel − LEVEL_STEP If TargetLevel < MIN_LEVEL ThenTargetLevel = MIN_LEVEL End If Else TargetLevel = TargetLevel +LEVEL_STEP If TargetLevel > MAX_TARGET_LEVEL Then TargetLevel =MAX_TARGET_LEVEL End If End If Prev_At_Speed = FALSE End If End If EndIf . . . Go to CONTROL LOOP

As may be appreciated from the foregoing, other algorithms andprogramming may be used to bring about the results described herein,such as is illustrated in FIGS. 1 and 2.

FIG. 3 shows a schematic of a hybrid electric vehicle in accordance withone embodiment of the present invention. FIG. 3 shows Internalcombustion engine 1 (e.g., Cummins ISB170 Diesel), Multi-speed automatictransmission 2, (e.g., Allison T2000 series), Ultracapacitor energystorage unit 3, (e.g., Maxwell BCAP series cells, 400 Volt maximum),Induction motor 4, (e.g., liquid cooled NEMA 215 frame, EVI Part205-0000), Induction motor inverter/controller 5, (e.g., IGBT-based EMSFluxDrive 7), Hybrid supervisory controller with CAN interface 6 (e.g.,8-bit microcontroller based, PIC18F248), Commercial truck chassis 7,(e.g., 15,000 pound GVWR, Workhorse Custom Chassis) and Vehicle controlnetwork 8 (e.g., Controller Area Network (CAN), SAE J1939 protocol).

FIG. 4 is a schematic representation of the control nodes that may beused in accordance with one embodiment of the present invention.

In accordance with the preferred embodiment, a parallel electric hybridis provided which uses ultracapacitors as the energy storage device. Aselectric power is transferred in and out of the bank of ultracapacitorsthrough successive discharge and charge events, the present inventionworks to maximize the usefulness of the ultracapacitor bank byregulating the minimum discharge set point.

As indicated above, the major system components of the hybrid vehicleare linked together via an electronic data bus that allows for controland state messages to be passed freely between connected nodes (as shownschematically in FIG. 4). This embodiment uses a standard high-speeddata network commonly used in commercial medium and heavy duty truck andbus systems. The network is based on the Controller Area Network (CAN)topology commercially available from Robert Bosch and preferablyutilizes the Society of Automotive Engineers (SAE) J1939 softwareprotocol which dictates a message bit rate of 250K bits per second andmessage addressing conventions.

Conventional medium and heavy duty vehicles typically link the engine,transmission, and brake systems on the network for control and datasharing. Tens of standard messages are broadcast by these nodes severaltimes per second. The hybrid components of this embodiment also use thiselectronic network. Nodes key to the present invention that link themotor drive and the hybrid supervisory controller to the network areadded. Other hybrid component nodes which supplement the supervisorycontroller are also added. These include a brake pedal module, adashboard/display module, an ultracapacitor module, and a motor/gearboxmodule.

The supervisory controller of this embodiment is an electroniccontroller that accepts and transmits data messages from the network andexecutes algorithms to elicit behavior from the motor drive, engine, andtransmission of the vehicle, although equivalent controllers may beused. This behavior creates the expected hybrid performance, such assupplanting engine torque with motor torque under acceleration andsupplanting friction braking with reverse motor torque underdeceleration. Also, the present invention allows an optimizing of theuse of the hybrid energy storage unit.

The controller preferably is based on an 8-bit microcontroller fromMicrochip, the PIC18F248. The algorithms of the present invention aretranslated from a high-level programming language, such as C or Basic,to machine code that can be written to the microcontrollers FLASHprogram memory. For instance, the algorithms are coded into Basic,compiled into Assembly language, then assembled and linked into machinecode for the particular PIC device. The machine code, typically in theform of a string of hexadecimal numbers, is then programmed into theFLASH memory of the target microcontroller using a hardware programmingdevice. Once programmed, the microcontroller begins execution of thealgorithms immediately after power is applied.

Vehicle speed and potential level of the energy storage device, in thecase of ultracapacitors, Voltage. The state of charge (or energy state)of the ultracapacitor follows directly the following relation,energy=½*capacity*potential²,where energy is in Joules, capacity is in Farads, and potential is inVolts.

Assuming that the capacity of the device does not change with operation,it can be seen that the energy level of the device is directlyproportional to the square of the potential, or of voltage. Therefore, asimple measure of the ultracapacitor voltage can allow one to derive theenergy level rather easily and is the basis of the algorithm of thepresent invention. The capacity of the ultracapacitor or similar energystorage device can be obtained experimentally or by consulting themanufacturer's specifications.

Aside from the 10 Hz control loop, the supervisory controller is alsoprogrammed to watch the network traffic on the CAN bus for messages ofinterest, particularly the ones cited above. When a message of interestis detected, the active process is interrupted and the message isdecoded and the data elements stored. This ensures that state parametersused in the algorithms, such as vehicle speed and ultracapacitorvoltage, are current.

During each pass of the control loop the state parameters and localvariables are evaluated and the algorithms executed. Simple examplealgorithms of the present invention are provided in pseudo code. Thealgorithm of the present invention can be made perhaps more effective byincorporating other sophisticated techniques. These techniques mayinclude predictive elements, the use of energy level instead ofpotential level for adjustment strategy, and others as indicatedelsewhere.

Many other changes and modifications may be made to the presentinvention without departing from the spirit thereof. The scope of theseand other changes will become apparent from the appended claims.

1. A method of controlling an energy storage system, said methodcomprising: providing a power unit and an electric energy storage systemelectrically coupled to an electric motor, said electric energy storagesystem adapted to recapture energy from the braking of said vehicle soas to be capable of discharging and recapturing energy through a seriesof discharge and energy recapture events, and having a maximum chargelevel and an actual minimum charge level; and wherein said power unitand said electric energy storage system provide electricity to saidelectric motor for powering said vehicle; and an electric energy storagecontroller programmed to control said electric energy storage system bysetting an artificial minimum charge level to an initial level abovesaid actual minimum charge level, and, during a series of discharge andenergy recapture events, to be able to adjust said artificial minimumcharge level such that: (a) in cases where a discharge and energyrecapture event results in the recapture of insufficient energy torecharge said electric energy storage system to said maximum chargelevel, raising said artificial minimum charge level; and (b) in caseswhere a discharge and energy recapture event results in the recapture ofsufficient energy to recharge said electric energy storage system tosaid maximum charge level, lowering said artificial minimum chargelevel.
 2. An energy storage system for an electric motor, said energystorage system adapted to accept energy so as to be capable ofdischarging and accepting energy through a series of discharge andenergy acceptance events, and having a maximum energy state level and anactual minimum energy state level; and wherein said system comprises apower unit and an electric motor, said power unit and said energystorage system being adapted to provide electricity to said electricmotor; and an energy storage controller programmed to control saidenergy storage system by setting an artificial minimum energy statelevel to an initial level above said actual minimum energy state level,and, during a series of discharge and energy acceptance events, to beable to adjust said artificial minimum energy state level such that: (a)in the case where a discharge and energy acceptance event results in theacceptance of insufficient energy to replenish said energy storagesystem to said maximum energy state level, said artificial minimumenergy state level is raised; and (b) in the case where a discharge andenergy acceptance event results in the acceptance of sufficient energyto replenish said energy storage system to said maximum energy statelevel, said artificial minimum energy state level is lowered.
 3. Anenergy storage system according to claim 2 wherein said energy storagecontroller is further programmed to control said energy storage systemby restricting the raising of said artificial minimum energy state levelbeyond a predetermined level below said maximum energy state level. 4.An energy storage system according to claim 2 wherein said energystorage controller is further programmed to control said energy storagesystem by restricting the lowering of said artificial minimum energystate level beyond a predetermined level above said actual minimumenergy state level.
 5. An energy storage system according to claim 2wherein said energy storage system is selected from the group of: (1) atleast one ultracapacitor and (2) at least one hydraulic cylinder.
 6. Anenergy storage system according to claim 2 additionally comprising aninternal combustion engine and a generator adapted to provide energy tosaid energy storage system.
 7. A method of controlling an energy storagesystem, said method comprising: providing an energy storage systemelectrically coupled to a power conversion device, said energy storagesystem adapted to recapture energy from said power conversion device soas to be capable of discharging and recapturing energy through a seriesof discharge and energy acceptance events, and having a maximum energystate level and an actual minimum energy state level; and said energystorage system providing energy to said power conversion device, andsaid power conversion device adapted to supply energy to said energystorage system; and an energy storage controller programmed to controlsaid energy storage system by setting an artificial minimum energy statelevel to an initial level above said actual minimum energy state level,and, during a series of discharge and energy acceptance events, to beable to adjust said artificial minimum energy state level such that: (a)in cases where a discharge and energy acceptance event results in theacceptance of insufficient energy to recharge said energy storage systemto said maximum energy state level, raising said artificial minimumenergy state level; and (b) in cases where a discharge and energyacceptance event results in the acceptance of sufficient energy torecharge said energy storage system to said maximum energy state level,lowering said artificial minimum energy state level.